Near-field dynamics of broad area diode laser at very high pump levels

Near-field properties of the emission of broad area semiconductor diode lasers under extremely high pumping of up to ∼50 times the threshold are investigated. A transition from a gain to thermally-induced index guiding is shown under operation with single pulses of 300 ns duration. At highest output powers, catastrophic optical damage is observed which is studied in conjunction with the evolution of time-averaged filamentary near-field properties. Dynamics of the process is resolved on a picosecond time scale

Near-field characteristics of broad area diode lasers during catastrophic optical damage failure

One of the failure mechanisms preventing diode lasers in reaching ultra high optical output powers is the catastrophic optical damage (COD). It is a sudden degradation mechanism which impairs the device functionality completely. COD is caused by a positive feedback loop of absorbing laser light and increasing temperature at a small portion of the active material, leading to a thermal runaway on a nanosecond timescale. We analyze commercial gain-guided AlGaAs/GaAs quantum well broad area diode lasers in single pulse step tests. The near-field emission on the way to and at the COD is resolved on a picosecond time scale by a streak-camera combined with a microscope. In the final phase of the step tests the COD is occurring at ~50 times threshold current. The growth of the COD defect site is monitored and defect propagation velocities between 30 and 190 μm/μs are determined. The final shape of the damage is verified by opening the device and taking a micro-photoluminescence map of the active layer. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)

Near-field evolution in strongly pumped broad area diode lasers

Many applications such as pumping of solid state lasers or ignition of explosives require high optical output powers during a short period. Pulsed operated diode lasers meet these requirements. They can be driven at elevated power levels, well above the ones specified for continuous wave (cw) operation. The optical near-field intensity of a diode laser in this operation regime is a key parameter since it determines the beam properties of the device. High power AlGaAs/GaAs quantum well broad area diode lasers are subjected to single pulse step tests carried out up to and beyond their ultimate limits of operation. Laser near-fields are monitored on a picosecond time scale using a streak-camera setup during pulse currents of up to ∼50 times the threshold current. A transition from gain guiding to thermally-induced index guiding of the near-field is shown. Further power increase is prevented by catastrophic optical damage (COD). This sudden failure mechanism is studied in conjunction with filamentary properties of the near-field. The defect growth dynamics resolved on the picosecond time scale is used to gather inside into the physics behind COD. © 2012 SPIE

Near-field dynamics of broad area diode laser at very high pump levels

Near-field properties of the emission of broad area semiconductor diode lasers under extremely high pumping of up to ∼50 times the threshold are investigated. A transition from a gain to thermally-induced index guiding is shown under operation with single pulses of 300 ns duration. At highest output powers, catastrophic optical damage is observed which is studied in conjunction with the evolution of time-averaged filamentary near-field properties. Dynamics of the process is resolved on a picosecond time scale. © 2011 Author(s)

High-reliability MOCVD-grown quantum dot laser

4.7 W continuous-wave (CW) and 11.7 W quasi-CW output power have been demonstrated for laser diodes based on six-fold stacks of InGaAs/GaAs quantum dots. Lifetimes beyond 3000 h at 1.0 and 1.5 W output power and 50degreesC heatsink temperature were measured. The output power is limited by catastrophic optical mirror damage occurring at 19.5 MW/cm(2) on the front facet

Reliability of 70 nm metamorphic HEMTs

The reliability and degradation mechanisms of 70 nm gate length metamorphic InAlAs/InGaAs HEMTs for low noise applications will be presented and discussed. Based an a 10% g(ind m max) failure criterion, a median time to failure of 10(exp 6) h and an activation energy of 1.3 eV in air were found. By comparing the electrical device characteristics before and after stress, gate sinking, ohmic contact degradation, and hot electron degradation were found to be the major failure mechanisms. The stress induced platinum diffusion into the semiconductor was quantified by cross-section TEM

Reverse bias stress test of GaN HEMTs for high-voltage switching applications

The degradation of packaged GaN HEMTs for high power applications has been studied under long term reverse bias step stress tests. Increases of leakage current and dynamic Ron resistance have been found. This degradation is possibly caused by the formation of localized defects which have been observed by backside electroluminescence imaging. In addition the effect of device layout and substrate material on the dynamic Ron as well as its temperature, recovery behavior, and drain voltage dependence have been investigated on wafer-level. The recovery behavior and the temperature dependence indicate that the dynamic Ron resistance increase is caused by surface or buffer carrier trapping. By reducing the buffer trap density the dynamic Ron resistance was reduced. A slightly higher dynamic Ron of GaN HEMTs on silicon compared to transistors on SiC substrate has been observed

Reliability of GaN HEMTs with a 100 nm gate length under DC-stress tests

The reliability of AlGaN/GaN HEMTs with a gate length of 100 nm suitable for applications up to W-band frequencies has been investigated by on- and off-state DC-stress tests. The extrapolated life time measured using the constant current stress test exceeds 105 h at a base plate temperature of 125°C. Very promising reliability results have also been found for the current step-stress tests even at the highest stress level of a DC power density of 12 W/mm. During off-state step-stress test the drain current exceeds the gate current indicating the onset of a buffer leakage current at drain voltages above the operation voltage

Next generation 8xx nm laser bars and single emitters

Semiconductor lasers with emission in the range 790 - 880 nm are in use for a variety of application resulting in different laser designs to fulfill requirements in output power, operation temperature and lifetimes. The output power is limited by self heating and catastrophic optical mirror damage at the laser facet (COMD). Now we present data on bars fabricated with our new facet technology, which enables us to double the maximum facet load. We present q-cw laser bar with 80% fill factor with increased power level to 350W in long term operation at 200s and 100Hz. The COMD limit of the bar is as high as 680W. Using Quantel's optimized packaging stacks with 11 bars of 5mm widths are tested at up to 120A resulting over 66% power conversion efficiency at 1600W output power. Laser bars for continuous wave operation like 50% fill factor bars had an COMD limit of approx. 250W with conventional facet technology, the value is equivalent to 10W per 200m emitter (conditions: 200s ). The new facet technology pushes the facet stability to 24W/emitter. The new process and an improved design enable us to shift continuous wave operation at 808nm from 100W to 150W/bar with lifetimes of several thousand hours at 30°C using DILAS mounting technology. Higher power is possible depending on lifetime requirements. The power conversion efficiency of the improved devices is as high as 62% at 200W cw. The next limitation of 8xxnm lasers is high temperature operation: Values of 60-80°C are common for consumer applications of single emitters. Therefore Osram developed a new epitaxial design which reduced the generation of bulk defects. The corresponding Osram single emitters operate at junction temperatures up to 95°C, a value which corresponds to 80°C heat sink temperature for lasers soldered on C-mount or 65°C case temperature for lasers mounted in TO can. Current densities of the single emitter broad area lasers are as high as 1.4kA/cm2 at 850nm emission wavelength